In many legacy telecommunications networks, transmissions between two nodes in the network are accomplished using time-division multiplexing (TDM). TDM combines multiple data streams into one signal, thereby allowing the data streams to share the physical lines in the data path without interfering with one another. More specifically, as its name suggests, TDM divides the signal into a number of segments, each constituting a fixed length of time. Because the sending node assigns data to the segments in a rotating, repeating sequence, the receiving node may reliably separate the data streams at the other end of the transmission medium.
With the rapid development of modern packet-switched networks, however, TDM has gradually fallen out of favor as a preferred technology. For example, Voice-Over-Internet Protocol (VoIP) services have replaced many TDM-based services, given VoIP's flexibility, ease of implementation, and reduction in costs. Unfortunately, transitioning to IP-based services requires a service provider to incur significant expenses in expanding its infrastructure and replacing customer premises equipment.
Given the large initial investment, many service providers have been reluctant to make the transition from TDM-based services to corresponding services in packet-switched networks. TDM pseudowires allow service providers to gradually make the transition to packet-switched networks, eliminating the need to replace TDM-based equipment and drop support of legacy services. In particular, on the ingress end of a TDM pseudowire, a node converts the TDM signals into a plurality of packets, then sends the packets across a packet-based path, or pseudowire. Upon receipt of the packets, a node on the egress end converts the packets back into TDM signals and forwards the TDM signals towards their ultimate destination.
Although TDM pseudowires offer flexibility and reduce expenses, they also introduce problems specific to packet-switched networks. Unlike TDM connections, packet-switched networks do not include mechanisms to ensure that nodes in the network send and receive packets at a constant rate. As a result, packet-switched networks inherently introduce a problem known as packet delay variation (PDV). PDV is particularly problematic when using the packet-switched network to emulate a TDM connection, as a multiplexed TDM signal must strictly adhere to timing requirements to ensure proper separation of the streams at the receiving node. PDV can dramatically affect the timing of the signal and, therefore, result in loss of data and affect the user's quality of experience.
The playout buffer is one solution developed to address the problem of packet delay variation when emulating TDM connections. A playout buffer regulates packet delay variation by temporarily storing packets, then outputting the packets at regular intervals using a play-out algorithm. Existing playout buffers, however, fail to meet the exact delay specified by a service provider except when the specified delay is a multiple of the delay associated with each packet. As a result, these systems increase the chances of a buffer underrun or overrun and therefore increase the likelihood of loss of data or interruptions that negatively affect the end user's quality of experience.
For the foregoing reasons and for further reasons that will be apparent to those of skill in the art upon reading and understanding this specification, there is a need for a playout buffer for use in connection with TDM pseudowires that provides the delay specified by the user.